This invention relates generally to particular polymer compositions and, more particularly, to polymer compositions incorporating interpenetrating polymer networks that provide for improved properties when used in a variety of products.
Interpenetrating polymer networks (IPNs) are described in a number of sources, including L. H. Sperling, Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York & London (1981). IPNs are defined as “a combination oftwo or more polymers in network form.” They can also be described as crosslinked polymer networks held together by permanent entanglements. The networks are held by “topological bonds,” essentially without covalent bonding between them.
The most important types of IPNs are semi- and full-IPNs. A full (or true) interpenetrating polymer network is a material containing two polymers, each in network form, with the two polymers having been polymerized or vulcanized independently in the presence of each other to form two networks, which are inter-tangled (interpenetrated) with each other. Semi- (or pseudo-) IPNs have only one crosslinked phase or network within a continuous unlinked polymer matrix phase. It is possible with certain solvent soluble resins to extract this non-crosslinked phase; this is not possible with a true IPN. As a result, true IPN systems must be cast, because once the components are admixed and polymer formation takes place, the interpenetrating networks cannot be separated. In contrast, the single crosslinked network of the semi-IPNs allows these materials to retain their thermoplastic character, although semi-IPNs with thermosetting properties also are possible. The IPNs may be formed using a number of different methods, including the synthesis (polymerization) and/or crosslinking (vulcanization) of the two polymers, taking place sequentially or simultaneously.
IPN technology is well-known in the prior art. IPNs were used industrially before being understood theoretically. The term IPN was introduced in 1960 in the first scientific study of IPNs (polystyrene networks) in J. Chem. Soc. (1960) 263, 1311. Dow Corning patented IPN structures in 1970 in U.S. Pat. No. 3,527,842 to obtain pressure-sensitive adhesives incorporating two polysiloxane networks.
Polysiloxanes have many interesting properties, but they possess low mechanical strength. Within IPN structures, polysiloxanes can be closely and permanently combined with a variety of polymeric materials, which can improve mechanical and physical properties significantly.
Additional patents providing relevant disclosures are discussed briefly below.
U.S. Pat. Nos. 4,500,688 and 4,714,739 disclose silicone systems that are vulcanized within a thermoplastic matrix such as polyamides, polyurethanes, styrenics, polyacetals and polycarbonates, to form semi-interpenetrating polymer networks that are either pure silicone polymers or hybrids of a silicone polymer and a non-silicone (e.g., vinyl) polymer. The vinyl-containing silicone is vulcanized in the thermoplastic during melt-mixing according to a chain extension or crosslinking mechanism that employs a silicon hydride-containing silicone component.
U.S. Pat. No. 4,695,602 discloses composites wherein a silicone semi-IPN vulcanized via a hydrosilation reaction is dispersed in a fiber-reinforced thermoplastic resin having a high flexural modulus.
U.S. Pat. No. 6,013,715 teaches the preparation of thermoplastic silicone elastomers wherein a silicone gum (or filled silicone gum) is dispersed in either a polyolefin or a poly(butylene terephthalate) resins and the gum is subsequently dynamically vulcanized therein via a hydrosilation cure system. The resulting elastomers exhibit an ultimate elongation at break of at least 25% and have significantly improved mechanical properties over the corresponding simple blends of resin and silicone gum in which the gum is not cured (i.e., physical blends).
U.S. Pat. No. 6,281,286 discloses that the impact resistance of polyester and polyamide resins can be greatly augmented by preparing a thermoplastic silicone vulcanizate. Although the resulting thermoplastic materials have improved impact resistance, they do not exhibit sufficiently low modulus to be useful as elastomers.
Polymer blends are particularly common in sporting goods, including athletic shoes, skis and ski equipment, snowboards, skates and skating equipment, bicycle components, football equipment, hockey equipment, soccer equipment, protective body gear, protective eyewear, golf clubs, and golf balls. Golf balls, in particular, extensively utilize polymer blends. Golf balls generally are constructed to include a core, at least one cover layer surrounding the core, and optional intermediate layers between the core and cover. A variety of polymer resins and blends of these resins are used to prepare compositions for making these layers. These resins are selected to optimize various ball properties, including speed, spin rate, and durability as demonstrated by shear-cut resistance.
In particular, ball covers have been prepared from balata, trans-polyisoprene (“synthetic balata”), thermoplastic polyurethane, thermoset polyurethane, and ionomer, or blends of these. Golf balls incorporating balata covers provide for a soft “feel” when hit and high spin rate, which improves ball controllability, but they also exhibit poor shear-cut resistance. Examples of golf ball covers incorporating balata and additional materials are disclosed in U.S. Pat. No. 4,984,803 to Llort et al. (“the Llort patent”) and U.S. Pat. No. 5,255,922 to Proudfit (“the Proudfit patent”). The limitations of use of balata in covers with respect to poor shear-cut resistance are described in the Llort and Proudfit patents, as well as in U.S. Pat. No. 6,042,489 to Renard et al. and U.S. Pat. No. 6,368,236 to Sullivan et al.
To address the limitations of balata, other materials have been used in ball covers. For example, ball covers have been made incorporating high acid-content copolymeric ionomers, such as those disclosed in U.S. Pat. No. 5,298,571 to Statz et al. These covers provide for balls having superior durability and speed when hit, but they also provide poor “feel” and low spin rate. Covers also have been made from blends of copolymeric and terpolymeric ionomers, such as those disclosed in U.S. Pat. Nos. 5,120,791 and 5,328,959, both to Sullivan. These covers demonstrate improved feel and spin rate compared to those made only from copolymeric ionomers, and they exhibit reduced, but acceptable, shear-cut resistance and ball speed. However, use of these ionomers does not provide for complete flexibility. lonomers exhibit ionic clustering, in which the metal cation-reacted functional groups cluster together due to the ionic attraction of the functional groups and the metal cations. This clustering is important in determining the physical properties and processability of the ionomers. However, ionomers as prepared have fixed levels of acid content and degree of reaction of the metal cation. As a result, the amount of ionic clustering in the particular ionomer, and the effect on properties of the ionomer, cannot readily be controlled.
In addition to use of balata and ionomers, covers also have incorporated thermoset polyurethane, such as is those disclosed in U.S. Pat. No. 6,132,324 to Hebert et al (“the Hebert patent”). Thermoset polyurethane covers provide good durability, feel, and spin rate, but these covers require complicated processing steps to mold the cover layer and to bring a full cure of the layer, as are described in the Hebert patent and in U.S. Pat. No. 6,328,921 to Marshall et al. Use of thermoplastic, rather than thermoset polyurethane, is described in, for example, U.S. Pat. No. 6,251,991 to Takasue et al. U.S. Pat. No. 6,369,125 to Nesbitt. Covers incorporating thermoplastic polyurethane provide for good feel, spin rate, and greater processability than thermoset polyurethane, but at the cost of poor shear-cut resistance. Also, the processing window (i.e., the range of suitable conditions for processing of the material) for thermoplastic polyurethane generally is narrower than for other thermoplastics used in making golf ball layers, leading to difficulties in manufacture.
Yet another approach for making golf ball cover compositions is to blend copolymeric or terpolymeric ionomers with elastomers. Such cover blends are disclosed in, for example, U.S. Pat. No. 6,371,869 to Kato et al. These blends provide good feel and high spin rate but, like blends of copolymeric and terpolymeric ionomers, they also provide for low shear-cut resistance and reduced ball speed. Additionally, blends of ionomers and elastomers can exhibit incompatibility between these components, leading to deterioration of ball performance and the need to use compatibilizers. Use of compatibilizers is described in patents discussed above, and also in, for example, U.S. Pat. No. 6,274,669 to Rajagopalan (golf ball covers incorporating ionomer blended with non-ionomer and compatibilizer).
Besides their use in ball covers, polymer blends also are used in golf ball cores, and in intermediate layers in multi-layer golf balls. The composition and resulting mechanical properties of the core are important in determining the ball's coefficient of restitution (C.O.R.), i.e., the ratio of the ball's post-impact to pre-impact speed, and its PGA compression, i.e., a measure of the deflection on the surface of the ball when a standard force is applied. A high C.O.R. improves ball speed and distance when hit, and generally, a high C.O.R. is achieved by having a high PGA compression. Golf ball cores generally are made from blends incorporating polybutadiene rubber. A number of patents discuss polymer blends for use in golf ball cores. For example, U.S. Pat. No. 6,239,222 to Nesbitt discloses cores comprising polybutadiene rubber and polypropylene powder resins. Also, U.S. Pat. No. 5,834,546 to Harris et al discloses cores comprising polybutadiene rubbers and oxa acids, and U.S. Pat. No. 6,426,387 to Kim discloses cores comprising cobalt-catalyzed polybutadiene rubber having specified material properties. Many different compositions are used, either of multiple polybutadiene rubbers, or of rubbers with other compounds, to prepare ball cores having optimal properties.
The composition of intermediate layers is important in determining the ball's spin rate and controllability. These intermediate layers often are made using soft or hard ionomeric resins, elastomeric resins, or blends of these, similar to those used in cover layers. Like blends for golf ball covers, polymer blends for cores and intermediate layers are prepared generally by dry-blending and/or melt-mixing of the component polymers, along with any required additives or fillers. Examples of polymer blend compositions for intermediate layers are described in a number of patents, including U.S. Pat. No. 6,355,715 to Ladd, which describes an intermediate layer comprising polyether-type polyurethane and a second thermoplastic component, such as a block copolymer, dynamically vulcanized thermoplastic elastomer, or other listed components. Also, U.S. Pat. No. 5,253,871 to Viollaz describes intermediate layer compositions incorporating amide block copolyether and ionomer, and U.S. Pat. No. 6,124,389 to Cavallaro et aL describes intermediate layer compositions incorporating an ethylene methacrylic/acrylic acid copolymer and other specified thermoplastic components.
As discussed above, additional examples exist of use of blends of polymers in a variety of goods, prepared using a number of known techniques. Despite this wide variety, blending of these polymers has a number of disadvantages. Processing of the polymers can be difficult because of poor processability of selected polymers. Also, incompatibility of different polymers can lead to phase separation of the base polymers in the blend, with resulting deterioration of blend properties. Also, despite the wide array of available polymers, tailoring polymers to be used in blends to have optimum properties can be difficult. Any attempt to create a blend to meet a specific set of criteria is limited by the available materials and available methods for forming these materials. That is, despite the wide variety of polymer blends known, there continues to be a lack of ease and flexibility in preparing tailored polymer blends. In view of the above, it is apparent that a need exists for improved methods for preparing polymer blends that provide for good processability, and tailoring of blend properties. The present invention fulfills this need and other needs, and provides further related advantages.